Illumination devices such as, for example, backlighting arrangements for displays or luminous means for Luminas generally comprise, for generating mixed-color light, primary light sources of different colors, the light of which is mixed additively.
If the brightnesses of the primary light sources are subject to fluctuations on account of external influences such as, for example, temperature changes or ageing processes, the color location of the mixed-color light on the CIE standard chromaticity diagram is shifted undesirably. In order to keep the color location of mixed-color light constant, feedback control systems have been proposed which measure the brightnesses of the different color channels with the aid of color sensors and determine and control the resultant color location.
Color sensors are components which can detect electromagnetic radiation of a limited wavelength range. They may comprise a photodiode, for example, which is provided with a color filter, so that said photodiode only detects light of a specific spectral range.
Descriptions of color sensors, and also application examples for calibration systems and feedback control systems for displays which use color sensors can be found for example at www.mazet.de/doc1/app99112.pdf,    www.mazet.de/doc1/app03121.pdf,    www.mazet.de/doc1/app99114.pdf and    www.taosinc.com/downloads/pdf/tcs230wp.pdf.
Color sensors have a series of disadvantages, however, which may lead to inaccuracies in the brightness measurements and increase the complexity of the control system. Thus, only color sensors with specific detection ranges are available commercially. Therefore, the detection range is rarely coordinated precisely with the spectrum of the primary light sources. Moreover, the limits of the detection range have a profile that usually runs in continuous fashion and not in sharply delimited fashion.